THE NAUTILUS. 137 
Of the seven possible variations from the normal arrangement, 
but four were noticed. Inno case were the cardinals alone reversed, 
but invariably a reversal of these teeth was accompanied by a 
reversal of either one or both pairs of laterals. Neither were the 
cardinals and posterior laterals alone, nor both pairs of laterals 
alone reversed in any case. The following table gives the details of 
the different variations observed and their relative frequency. 
Normal Spherium—cardinals } Ant. Lat. 7 Post. Lat. ?. 
Abnormal S. striatinuwm Lam. 
No. of specimens 22: Cardinals } Ant. Lat. 3 Post. Lat. 2. 
No. of specimens 32: Cardinals ? Ant. Lat. 3 Post. Lat. 2. 
No. of specimens 22: Cardinals? Ant. Lat. 3 Post. Lat. 3. 
No. of specimens 32: Cardinals} Ant. Lat. 2 Post. Lat. 4. 
Abnormal S. simile Say. 
No. of specimens 52: Cardinals ? Ant. Lat. } Post. Lat. 
No. of specimens 32: Cardinals ? Ant. Lat. } Post. Lat. 
No. of specimens 22: Cardinals } Ant. Lat. ? Post. Lat. 
nie NH rite 
NEW AMERICAN ANCYLIDE. 
BY HENRY A. PILSBRY. 
Owing doubtless to the difficulty of distinguishing species in this 
group, but little work has been done upon the United States forms 
since the publication of Haldeman’s monograph in 1842. Clessin, 
in the “Conchylien Cabinet,” has added nothing of value to our 
knowledge of United States species, his A. oregonensis from Salem, 
Oregon, of which I have “ topotypes,” being doubtfully distinct from 
Tryon’s A. fragilis. A. caurinus is also, as Tryon states, a synonym 
of fragilis. 
In naming a series of Illinois mollusks for the Illinois State Lab- 
oratory of Natural History, my attention was directed to this genus. 
The species of Ancylus fall into two groups, not, I suppose, of 
much importance systematically, but of considerable interest in a 
broad view of the conditions of mollusk life. One group, which 
may be termed the “ petrophilous” Ancyli, live on rocks and shells 
in rivers, and usually have a rather highly conic shell. The other 
group, “ phytophilous ” Ancyli, live on water plants; some deeply 
submerged, as on the “leaves of grass” (to use a Walt. Whitman- 
ism), streaming upward from the bottom ; others inhabit the round 
